xen setup/config

["Chris Vella" <chris@dload.com.au>]

A little help please guys or a pointer in the right direction for a
configuration/setup recommendation. 

Whilst I have been using the XEN hypervisor in our office/dev environments
for some time, I am preparing to deploy the latest XCP/Xen build for our
live/collocation installation. 

To date I haven't used any virtualisation at all in our live environment.
Our setup is relatively straightforward with a physical three tier model: 

. Presentation tier (web servers, smtp, etc.)
. Logic tier (business and operational servers)
. Data tier (database and storage)

I am going to leave the Data tier non virtualised and virtualise (compress)
the logic and presentation tier onto the same physical hardware. 

So the example scenario is:

. Both the Presentation and Logic tiers currently have 6 physical servers
each (12 total) in a load balanced (shared nothing) arrangement. These will
be replaced with 3-4 physical servers running at least two VM's on each.
. How would you set up the XEN environment for dynamic workload structures? 
. If spikes come through via the presentation tier how do you prioritise
CPU/bandwidth to these servers/VM's?
. Likewise if the presentation tier is acquiescent then how do you control
it such that if the logic tier gets busy it can consume idle CPU/bandwidth?


Regards,

Chris